1. Field of the Invention
Embodiments of this invention relate to novel internally cooled magnetic resonance imagining (IC-MRI) coils, cryogenic apparatuses including the IC-MRI coils and to method for making and using same. Embodiments of the invention also relate to balanced and symmetrically grounded IC-MRI coils.
More particularly, embodiments of this invention relate to novel internally cooled MRI (IC-MRI) coils, resonators, cryogenic apparatuses including the IC-MRI coils, where the IC-MRI coils are constructed so that a coolant (in certain embodiments, a cryo-coolant) circulates through an interior of the coils, through the interior of a substrate on which the coils are mounted, or through both the coils and the substrate, where the electric fields generated by the coils are zero or negligibly small. Embodiments also relate to balanced and symmetrically grounded IC-MRI coils. Embodiments of the invention also relate to methods for making and using the IC-MRI coils, and/or cryogenic apparatuses including the IC-MRI coils.
2. Description of the Related Art
Since the inventions of magnetic resonance imaging (MRI) in 1973, significant advances and developments of this method has turned it into a widely used clinical and research tool, which provides an unsurpassed, non intrusive technique to image soft tissues. The MRI is related to the phenomenon of nuclear magnetic resonance (NMR), which is based on the excitation and relaxation of nuclei (most frequently protons) within living tissues in a DC magnetic field. An excitation repulse at the Larmor frequency v, which is the precession frequency of protons in DC magnetic field (ν=63.8 MHz for 1.5 Tesla), disturbs the equilibrium state of the nuclei. After the repulse, the nuclei relax to the equilibrium state with two different relaxation times (T1 and T2) and produce a weak decaying of signal.
In a MRI set-up, these weak decaying rf signals are detected by a receiver probe. For diagnostic usefulness of this signal, its level has to be well above the noise level, thus it puts premium on signal-to-noise ratio (SNR) of the receiver probe. In small volume MRI, MRI microscopy, low-field MRI, and NMR spectroscopy it has been shown that the Johnson noise of the rf receiver probe and/or preamplifier dominates, and thus determines the system noise floor.
In recent years, the design of phased arrays for parallel acquisition in MRI application has become the subject of a great deal of research. The drive for faster and faster acquisition rates calls for arrays with large number of receiving elements. As the number of array elements increases and their size continues to decrease, conductive losses become more dominant. These losses can overwhelm any signal-to-noise ratio (SNR) gains expected from the use of smaller coils that express less body noise.
As the need for higher signal-to-noise ratio and greater resolution increases, the benefit from using cryogenic and/or superconducting coils greatly depends on the ratio between coil and body noise. Although many different MRI systems exist, each has a specific coil/body noise ratio that depends on frequency of operation and coil size.
Prior art MRI probes exist in a variety of geometrical configurations. U.S. Pat. No. 5,699,801 to Atalar discloses an MRI probe having pair of electrodes arranged in a parallel configuration and embedded within a dielectric material.
U.S. Pat. No. 4,672,972 to Berke discloses an NMR probe embedded within a probe head region disposed at the distal end of a catheter/endoscope.
U.S. Pat. No. 6,171,240 to Young et al. discloses a radio frequency (ARF.congruent.) probe adapted for use in MRI comprising a loop of an elongated electrical conductor arranged to form a twisted wire pair and a means for operating the probe in a transmit and receive mode for intraluminal MRI.
U.S. Pat. No. 7,511,497 disclosed superconducting array of surface MRI probes and U.S. Pat. No. 6,950,063 disclosed intraluminal MRI probe.
Thus, there is a need in the art for novel internally cooled magnetic resonance imaging (IC-MRI) coils and new apparatus utilizing such IC-MRI coils, where a coolant circulates through an interior of the coils, through a substrate on which the coil are formed, or through both.